A disk-type braking system comprises a ventilated or non-ventilated metal disk, which is rigidly fixed on the rotating hub of the wheel so as to be driven in rotation therewith.
The disk is mounted perpendicularly to the rotation axis so that its plane traverses the plane of symmetry of a caliper fixed on the hub-carrier. The caliper is provided on its flanges in opposite relationship, with two brake linings which are placed on either side of the faces of the disk astride which is placed the caliper. Hydraulic pistons actuate the linings in order to move them in opposite directions and to clamp the disk, for the purpose of stopping its rotation.
A braking device of the above type is an unquestionable improvement over the prior mechanisms, called drum brakes. Yet, such device cannot be considered as fully satisfactory for the following reasons.
Because of the mounting method used, the disk and the caliper are not directly coupled to metallic masses capable of inducing the evacuation of the calories produced by the energy dissipated by the braking action. Therefore they are subjected to overheating in cases of intensive use. An excessive rise in temperature, particularly of the disk which is generally made of metal, may be damaging to the general structure and affect braking efficiency.
With the mounting method used, the caliper is brought in contact with the disk subjected to the rise in temperature. The resulting overheating is therefore also applied to the pistons which are hydraulically actuated for clamping the linings on either sides of the disk. Overheating of the hydraulic fluid controlling the pistons may cause a failure of the braking operation if the oil vapors, released as a result, are sufficiently strong to induce the phenomenon known as vapor-lock.
The efficiency of a disk-brake is more dependent on the active surface of the linings than on that of the rotary disk. Therefore, by construction, such efficiency is limited, given that, up to the present time, the serviceable surface of the lining or linings, or even of the successive sets of plates used, is always smaller than the friction surface presented by a rotary disk.
However, a mounting of the aforesaid type, which can be considered as simplified compared with the prior drum-type systems does not give a particularly easy access to the friction linings which, as wear elements, require to be replaced periodically.
Experiments, conducted up to now, have shown that a brake of the aforesaid type is subjected, particularly when the disk is produced in a wear material, to an oxidation on all its relative part which is not covered by the linings. The oxidation of such materials increases the wear to considerable proportions.
It is also known from the prior art, particularly from patent application DE-B-1 075 447, to use a disk brake of the type comprising one rotor disk driven in rotation by the hub of a wheel, and two stator disks placed on either side of said rotor disk. One of the stator disks is moved by an annular cylinder in order to achieve the clamping of the rotor disk.
And it is also known from patent application DE-A3 009 006, to use a disk comprising a rotor, driven in rotation by the wheel hub and presenting a friction face on the hub side. The brake also comprises a stator disk supported by the hub-carrier of the wheel and presenting a friction face on the wheel side, which face is situated in facing relationship and very close to that of the rotor disk. The stator disk can be moved by an annular cylinder along a direction parallel to the hub axis.
In addition to the fact that the two above-described brakes are definitely subjected to overheating, which affects the braking efficiency, it appears that their mounting does not allow ready access to the different wear elements provided in such brakes.